Admittedly I’m biased.
Having shot, and lost, a goodly number of deer with the .243, I’ll venture there is a considerable difference between the .243 and .257Roberts, but NOT with most available FACTORY ammo. My current kill count with the “Bob” is over 100 deer ranging from 70lb yearlings to the largest buck I’ve ever killed (over 250lbs) closer to 200, if I add in the .25-36Marlin and .257wbymag.
Several reasons:
1. To quote writer John Barsness, most Factory .257Robt. is loaded to the pressure levels of a “burrito fart”. Think U.S. manufactured 8x57 Mauser. Weak!
My handloads almost exactly match those of J.B.’s, though we were doing the same things at the same time over a 1,000miles apart.
2. Again, to quote an article by J.B. in HANDLOADER a number of years back on conventional cup-and-core bullets, there is a significant difference in the friction/tension of the jacket to core fit with the larger .257” bullets. His observations closely match my experience.
Simply put, the .257 with similar weight bullets at similar pressures kills better than the .243. No surprise, really.
But here’s the twist; because of current dearth of brass for the .257, a new shooter will have difficulty getting into loading the .257.
There is a abundance of .243 ammo and components. Very slight advantage to .243.
But, personally, If you reload; get some 100-120gr bullets for your .270, and some H4895 and load 40-45gr to get 2,800-3,000fps. This will give recoil identical to a.243/.257 but kills just as good as your current.270 loads. If you don’t reload, Remington makes an excellent “Reduced Recoil” load that will tame your .270.
But really? The whole deal about the .270 is it recoils less than the ‘06. I don’t find the .270 to recoil that much more than a .243/.257.
If recoil is that big of a deal, I suggest a good .223 with a fast twist barrel and a 60-70gr soft point bullet. I actually have had better on-game performance from the .22’s than the .243. The Ruger American Predator in .223 w1/9” twist with the Hornady 60gr Spt comes to mind. The deer in my avatar fell to a Hornady 60gr Spt (MidwayUSA blem!) at ~2,900fps Christmas Day ‘17 fired from my Rem Mod-7. Shot it out my kitchen window at a lased 141yds.
Most important is 1. Shot placement 2. Shot placement 3. Shot placement. If recoil reduction helps, do it! How, is your decision.
But, I suspect you are just trying to justify a new rifle. BTDT!